1. Field of the Invention
The present invention relates to a technology of reducing a metallic artifact by extracting a position of a metallic body included in a CT photographic region in X-ray CT photography.
2. Description of the Background Art
Conventionally, the X-ray CT photography is performed in a medical field and the like. In the X-ray CT photography, a subject is irradiated with an X-ray to collect its projection data expressing a projection image, and the projection data is reconstructed on a computer to generate a CT (Computed (Computerized) Tomography) image (tomographic image).
In the X-ray CT photography, the subject is disposed between an X-ray generator and an X-ray detector, the X-ray generator and the X-ray detector turn about the subject, and the X-ray generator emits the conical X-ray (an X-ray cone beam) to the subject. The X-ray detector collects detection result (projection data) of the X-ray, and CT image data (volume data) is reconstructed based on the collected detection result of the X-ray.
In the case that a metallic body having a high X-ray absorption factor is included in the CT photographic region, the X-ray is hardly transmitted through the metallic body, and a correct transmission amount is hardly measured. Therefore, sometimes many streak noises (metallic artifacts) are generated around the metallic body on the CT image (the tomographic image) that is obtained by reconstructing the projection data. In the case that the metallic artifact is generated, a correct image diagnosis is hardly performed. Therefore, some methods of removing the metallic artifact have been proposed (for example, see Japanese Patent Publication Laid-Open No. 2010-099114).
Specifically, in the technology disclosed in Japanese Patent Publication Laid-Open No. 2010-099114, a metal position is specified by binarizing a sinogram generated from the projection data using a predetermined threshold.
However, in this technology, it is necessary to properly set the threshold in order to separate a metallic portion from a non-metallic portion. Therefore, in the case that the threshold is improperly set, possibly the metallic artifact cannot properly be removed because the metal position is hardly specified with high accuracy.